1. Field of the Invention
The present invention relates to a paper-threading device for threading paper web along a paper-threading path, along which paper web travels during operation of a rotary press. More particularly, the invention relates to a paper-threading device for threading paper web along an angle-bar paper-threading path by means of moving a paper leader to which paper web is affixed, along a paper-leader guide provided along the angle-bar paper-threading path, which extends around angle bars while changing direction at each angle bar.
2. Description of the Related Art
A conventional automatic paper-threading device for use in an angle bar section of a rotary press is disclosed in, for example, Japanese Utility Model Publication (kokoku) No. 7-39646.
This automatic paper-threading device includes a guide pipe having a cross section shaped like the letter C and a paper-threading rope movably accommodated in the guide pipe. The guide pipe is provided along an angle-bar paper-threading path, which extends around angle bars while changing direction at each angle bar. A joint is attached to the paper-threading rope in such a manner as to be projected through a slit formed in the guide pipe. A paper web leader made from a film material is attached to the joint. A leading end portion of paper web is affixed to the paper web leader. The paper-threading rope is caused to travel through the guide pipe by means of a driving roller and an auxiliary roller, between which the paper-threading rope is held, thereby threading paper web along the angle-bar paper-threading path.
The paper-threading rope stands by at a position which is located upstream of the angle-bar paper-threading path and downstream of a slitter with respect to a traveling direction of paper web. The slitter slits paper web into two paper web strips. One paper web strip is transported by the paper-threading rope. When a sensor detects a leading end portion of the paper web strip, an affixing device is operated so as to affix the leading end portion of the paper web strip to the paper web leader. Thus, the paper web strip is threaded along the angle-bar paper-threading path.
As shown in FIG. 18, which shows the above-described conventional automatic paper-threading device, a gap must be provided between a guide pipe 9b and angle bars (first bar 23 and second bar 24). Thus, the guide pipe 9b extends along a route which is more distant from the angle bars than is the actual paper-threading path for a paper web strip 1c. As a result, as the paper web strip 1c passes the first bar 23 and then the second bar 24, its slack increases. Also, the paper web strip 1c tends to be drawn toward a paper-threading rope 10b. Specifically, when the leading end portion of the paper web strip 1c passes the first bar 23, a force acts on the paper web strip 1c in the direction of arrow m, since a force of pulling the paper-threading rope 10b, or a force directed in the direction of arrow k, is produced at the center of the guide pipe 9b.
A component force directed in the direction of arrow n of the above-mentioned force directed in the direction of arrow m causes the paper web strip 1c to move in the direction of arrow n while traveling in the moving direction of the paper-threading rope 10b (in the direction of arrow k). In an initial stage of a paper-threading process, an obliquely cut end portion of the paper web strip 1c is in contact with the first bar 23; in other words, the paper web strip 1c is not in contact with the first bar 23 across the entire width thereof. Accordingly, the contact area between the paper web strip 1c and the first bar 23 is small, and the paper web strip 1c is slack. Thus, a frictional resistance generated between the paper web strip 1c and the first bar 23 is low, so that the paper web strip 1c easily shifts on the first bar 23 in the direction of arrow q.
Because of the above-described two reasons, when the paper web strip 1c is threaded along the angle-bar paper-threading path while being looped around the first bar 23 and the second bar 24, the paper web strip 1c is drawn toward the paper-threading rope 10b. In some cases, the thus-drawn side edge of the paper web strip 1c may be caught between the paper-threading rope 10b and a driving roller 18a of a drive unit 18.
As a result of the obliquely cut leading end portion of the paper web strip 1c being drawn toward the paper-threading rope 10b, the above-mentioned slack of the end portion emerges in the form of waves in the longitudinal or lateral direction of the paper web strip 1c. Upon contact with the first bar 23 and the second bar 24, these waves become wrinkles, causing a nonuniform tension to act on the end portion, which is narrower than the regular width of the paper web strip 1c. As a result, the end portion may be torn.
Since the paper web strip 1c must be affixed to the paper web leader of the paper-threading rope 10b by means of an affixing device 43 (see FIG. 17) at a position located upstream of the first bar 23, the distance between a side edge of the paper-threading path and the guide pipe 9b, through which the paper-threading rope 10b travels, is narrower than that at a position located downstream of the second bar 24. Accordingly, as the paper web strip 1c is looped around the first bar 23 and then the second bar 24, the paper web strip 1c deviates increasingly farther from the paper-threading path.
Specifically, as shown in FIG. 18, the letter "H" represents the distance between the center of the paper-threading rope 10b and a side edge of the paper-threading path for the paper web strip 1c as measured in the vicinity of the affixing device 43; the letter "I" represents that as measured at a position located between the first bar 23 and the second bar 24; and the letter "J" represents that as measured at a position located downstream of the second bar 24. The distances H, I, and J exhibit the relationship "H&lt;I&lt;J," indicating that the distance increases as the paper web strip 1c travels forward. The letter "r" denotes the locus of an end portion p of the paper web strip 1c along the angle-bar paper-threading path.
The paper web strip 1c gradually deviates from the paper-threading path as it is threaded forward while being guided by the paper-threading rope 10b. However, the conventional automatic paper-threading device provides no particular measure against this.